Integrated circuit with tightly coupled passive components

ABSTRACT

A multi-component electronic assembly ( 100 ) including a leadframe ( 101 ) having upper and lower surfaces and a plurality of conductive leads ( 203 ). Each lead ( 203 ) has first bonding surfaces ( 201 ) on the upper surface of each lead and second bonding surfaces ( 201 ) on the lower surface of each lead ( 203 ). Preferably, each lead has a plurality of third bonding surfaces ( 202 ) formed on at least some of the plurality of leads where the third bonding surfaces ( 202 ) are formed by conductive extensions of the leads ( 203 ) that extend towards the center of the assembly ( 100 ). A first passive component ( 102 ) is electrically and mechanically coupled to the first bonding surfaces. A second passive component ( 104 ) is electrically and mechanically coupled to the second bonding surfaces. Where third bonding surfaces ( 202 ) are used, a third component ( 103 ) is electrically and mechanically coupled to the third bonding surfaces ( 202 ).

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a division of U.S. Ser. No. 08/992,701, filed Dec.17, 1997 which claims priority uner 35 U.S.C. 119(e) based uponProvsional Application Serial No. 60/034,260, filed Dec. 20, 1996 nowU.S. Pat. No. 6,054,764.

1. GOVERNMENT LICENSE RIGHTS

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of contract No.DAAL01-95-C-3525 awarded by DARPA.

BACKGROUND OF THE INVENTION

2. Field of the Invention

The present invention relates, in general, to multi-component electroniccircuits, and more specifically, to an assembly and method forassembling an integrated circuit that is tightly coupled to inductor andcapacitor elements on a single leadframe.

3. Relevant Background

Many passive components (e.g., capacitors, inductors and resistors)cannot be cost effectively integrated onto a monolithic integratedcircuit because of their size. Also, the limitations in a particularintegrated circuit processing technology may prohibit inductors or highvalued capacitors and resistors. Typically, large valued inductors andcapacitors are manufactured as separate components and interconnectedwith the integrated circuit to provide the desired functionality.

For example, in power supplies such as AC-DC and DC-DC converters, largevalue inductors and capacitors are required that cannot be provided onthe integrated circuit. Most such circuits are manufactured usingmultiple components interconnected by printed wiring on a circuit board.However, there is increasing demand for single device solutions forpower supply circuits to reduce overall system size.

It is desirable from a manufacturer's and user's standpoint thatpackaged circuits require as few external components as possible. Thiseases assembly and lowers costs for the end user while increasing valueadded to the manufacturer. Hence, integrated circuit manufacturers areincreasingly offering multi-component modules that include one or moreintegrated circuit chips packaged together with external passivecomponents such as inductive and capacitor elements.

Another advantage of multi-component packaging is that stray andparasitic capacitance and inductance associated with leads and circuitboard traces can be eliminated. However, stray capacitance andinductance associated with wire bonds connecting multiple chips remain aproblem. In conventional multi-component modules, components are mountedon a substrate or leadframe in the same plane and coupled together bywire bonds. This “planar” arrangement results in large packages makingthe packages more difficult to use, expensive to manufacture and costlyin terms of circuit board real estate for the user.

Some attempts have been made to vertically stack integrated circuitswith associated passive components. Some of these efforts require threedimensionally formed lead frames that are difficult to manufacture anddifficult to work with on an assembly line. Also, the integratedcircuits could be left exposed on the surfaces of the vertical stack.Moreover, existing vertically stacked assemblies require relativelydifficult assembly adding to the production cost of the component. It isdesirable to use planar lead frames and to avoid exposure of theintegrated circuit chip.

SUMMARY OF THE INVENTION

The present invention involves a multi-component electronic assemblyincluding a leadframe having upper and lower surfaces and a plurality ofconductive leads. The leadframe includes first bonding surfaces on theupper surface of each lead and second bonding surfaces on the lowersurface of each lead. Preferably, each lead has a plurality of thirdbonding surfaces formed on at least some of the plurality of leads wherethe third bonding surfaces are formed by conductive extensions of theleads that extend towards the center of the assembly. A first componentis electrically and mechanically coupled to the first bonding surfaces.A second component is electrically and mechanically coupled to thesecond bonding surfaces. Where third bonding surfaces are used, a thirdcomponent is electrically and mechanically coupled to the third bondingsurfaces.

Another aspect of the present invention is a leadframe having aplurality of leads, each lead having first, second, and third bondingsurfaces and having a terminal end for coupling the first, second andthird bonding surfaces to external electrical circuitry.

In another aspect the present invention involves a method for assemblinga multi-component electronic assembly including the steps of providing aleadframe having upper and lower surfaces and a plurality of conductiveleads. Each lead has first bonding surfaces on the upper surface of eachlead and second bonding surfaces on the lower surface of each lead.Preferably, at least some of the leads include a plurality of thirdbonding surfaces. A first component is electrically and mechanicallycoupled to the first bonding surfaces. A second component iselectrically and mechanically coupled to the second bonding surfaces. Athird component is electrically and mechanically coupled to the thirdbonding surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in perspective view a multi-component assembly inaccordance with the present invention;

FIG. 2 illustrates the multi-component assembly of FIG. 1 in an explodedperspective view;

FIG. 3 shows a leadframe useful in manufacturing multi-component circuitin accordance with the present invention;

FIG. 4 illustrates an integrated circuit chip for mounting on theleadframe shown in FIG. 3; and

FIG. 5 illustrates the integrated circuit of FIG. 4 mounted on aleadframe of FIG. 3.

In the various figures of the drawing, like reference numerals are usedto denote like or similar parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is illustrated in FIG. 1 as a power supply circuitassembly 100 that includes control circuitry formed on an integratedcircuit chip 103 assembled with passive components such as capacitorelement 104 and an inductor element 102. In a particular example,capacitor element 104 comprises a plurality of capacitors and inductorelement 102 comprises a plurality of inductors. Because of the largevalue of the capacitors and inductors, they cannot be efficientlyintegrated on the integrated circuit chip. The present invention uses aplanar leadframe 101 and vertically stacks the multiple components 102,103 and 104 about leadframe 101 to provide a highly compact tightlycoupled multi-component assembly 100.

As used herein, the terms “planar” and “coplanar” are used to describethe relationship of on the upper and lower sides of bonding surfaces 201as well as bonding surfaces 202 (shown and described in reference toFIG. 2). Although bonding surfaces 201 that are on opposite sides ofleadframe 101 are not truly planar, they are considered sufficientlycoplanar or planar for purposes of the present invention. After assembly100 is formed, leadframe 100 is typically trimmed to separate individualleads 203 that extend away from the body of assembly 100. Aftertrimming, the extended portions (i.e., the terminal ends) of leads 203are bent or formed so that they are no longer coplanar with bondingsurfaces 201 and 202 at the interior of assembly 100. As used herein,the terminal ends of leads 203 are not considered “bonding surfaces”even though they will be used to bond assembly 100 to external circuitrysuch as circuit boards.

While the present invention is described in terms of a-particularcircuit and is illustrated with some particularity with respect tocomponent shapes, sizes and interconnections, the teachings of thepresent invention are applicable to any multi-component assembly. Thepresent invention is particularly applicable to assemblies that requiretight coupling (i.e., little parasitic inductance between coupledcomponents) and assemblies in which small packaging is particularlyimportant. The particular materials described herein are provided forease of understanding only, and many equivalent materials are known inthe electronic assembly industry.

As shown in FIG. 1, leadframe 101 comprises a stamped or chemicallyetched substantially planar metal structure. Although a planar leadframe101 is a particular advantage of the assembly method in accordance withthe present invention, a non-planar leadframe can be used in combinationwith other features of the present invention while still achieving someof the advantages in accordance with the present invention.

Leadframe 101 is formed to have a plurality of leads 203 extending awayfrom the multi-component assembly 100. Leads 203 will be separated fromleadframe 101 during a late stage in processing and will provideinterconnects to external circuitry (not shown). Typically,multi-component assembly 100 would be encapsulated in an epoxy orplastic encapsulant or enclosed in a metal or ceramic case to provideenvironmental and physical protection to the components within assembly100.

In the preferred embodiment, the multi-component assembly includes acapacitor element 104 mounted to the lower surface of leadframe 101.Integrated circuit chip 103 is attached by, for example, solder bumps orconductive epoxy to mounting surfaces on the upper surface of leadframe101. Inductor element 102 is mounted to selected leads at mountingsurfaces set away from the mounting surfaces used to couple tointegrated circuit 103. A packaging material such as encapsulant 105 maybe used to seal and is protect assembly 100. Equivalently, assembly 100may be sealed in a metal or ceramic encasing or similar package.

FIG. 2 illustrates the structure shown in FIG. 1 in an explodedperspective view that eases understanding of the assembly process.Leadframe 101 includes a plurality of leads 203, some of which containmultiple bonding surfaces. First bonding surfaces 201 are positioned atthe outer periphery of subassembly 100. The lower surface of mountingsurface 201 is adapted to electrically and mechanically coupled tobonding pads of capacitor element 104. Capacitor element 104 may includeone or more capacitors that have capacitor terminals coupled to bondingpads 204. It is not necessary to use all of bonding pads 204 forelectrical connection. However, if fewer than all bond pads 204 arerequired, it is preferred to mechanically attach the unused bond pads204 to bonding surfaces 201 to provide mechanical support. In theparticular example shown in FIG. 2, capacitor element 104 has eightbonding pads 204 that would be mounted by solder bump bonds to thebottom surfaces of mounting surfaces 201.

The upper portion of mounting surfaces 201 is also used to electricallycouple to inductor element 205 and/or integrated circuit 103. In theparticular example at FIG. 2, inductor element 102 has four bonding pads205 coupled to inductor terminals within inductor 102. Inductor bondingpads 205 align with and bond to the upper surface of four of bondingpads 201. Integrated circuit 103 includes a plurality of bonding pads(not shown) that mount to the inner four bonding surfaces 201. It is notnecessary that electrical connection be made to all of inductor bondpads 203, however, it is recommended that all of bond pads 204 bemechanically attached to available bonding surfaces 201 to provide rigidconstruction.

Some or all of leads 203 also include second bonding surfaces 202.Second bonding surfaces 202 are aligned to and adapted to mount tointegrated circuit bonding pads on integrated circuit 103.

One feature in accordance with the present invention is that leadframe101 desirably provides bonding surfaces on both the upper and lowersurfaces (i.e., upper and lower bonding surfaces 201) of leadframe 101.In addition, multiple bonding surfaces are provided on each lead on anygiven side (i.e., bonding surfaces 201 and 202). This allows theleadframe 101 to form complex interconnections in both a horizontal andvertical direction. This efficient use of leadframe 101 gives tightelectrical and mechanical coupling between components in multi-componentassembly 100 and decreases the overall size of multi-component assembly100 through the use of vertically stacked components. Significantly,even though leadframe 101 is a substantially planar structure, itenables vertical interconnections among the components.

FIG. 3 illustrates leadframe 101 in greater detail. Leadframe 101 mayinclude any number of leads 203. Also, leads 203 may take any convenientshape to make interconnections to the various components. Each lead 203has at least two bonding surfaces and several leads 203 include threebonding surfaces. The first set of bonding surfaces comprises bondingsurfaces 201 located on the upper side of leadframe 101. The second setof bonding surface comprises bonding surfaces 201 on the lower surfaceof leadframe 101 for coupling to the capacitor element 104. Thirdbonding surfaces 202 are formed as extensions of leads 203 that extendinto the central portion of leadframe 101 and are adapted to couple tobond pads 401 (shown in FIG. 4) on integrated circuit 103.

Integrated circuit 103 is shown in greater detail in the plan view ofFIG. 4. Any type of circuitry may be formed on IC 103 in any availabletechnology. Bond pads 401 are preferably coated with a thin layer ofsolder or other flowable metal such as gold. Alternatively, conductivefilled polymer or epoxy may be used to enhance electrical couplingbetween bond pads 401 and bonding surfaces 202 (shown in FIG. 3).Integrated circuit 103 may also be implemented as multiple chips mountedadjacent to each other.

FIG. 5 shows IC 103 mounted to leadframe 101 in accordance with apreferred embodiment. It can be seen that some of bond pads 401 coupleto first bond surfaces 201. Others of bond pads 401 are coupled to thirdbond surfaces 202. This leaves exposed bond surfaces 201 on the uppersurface of leadframe 101 for coupling to inductor element 102. This alsoleaves all eight of the lower bond surfaces 201 under leadframe 101available for coupling to the eight bond pads of capacitor 104.

By now it should be appreciated that a central side leadframe design isprovided that allows vertically stacked components with using a planarleadframe. Because the planar leadframe is used, assembly costs arereduced. Because the integrated circuit component is sandwiched betweentwo passive components, it is protected from external environment. Themulti-component assembly 100 in accordance with the present inventionhence is more rugged and provides improved performance due to the tightcoupling and low inductance coupling between the integrated circuit andpassive components.

Although the invention has been described and illustrated with a certaindegree of particularity, it is understood that the present disclosurehas been made only by way of example, and that numerous changes in thecombination and arrangement of parts can be resorted to by those skilledin the art without departing from the spirit and scope of the invention,as hereinafter claimed.

What is claimed is:
 1. A method for assembling a multi-componentelectronic assembly comprising the steps of: providing a patternedleadframe having upper and lower surfaces and a plurality of conductiveleads, each lead having first bonding surfaces on the upper surface ofeach lead, second bonding surfaces on the lower surface of each lead,and third bonding surfaces on the upper surface of at least some of theplurality of leads; electrically and mechanically coupling an integratedcircuit to the first bonding surfaces; electrically and mechanicallycoupling a first passive component to the second bonding surfaces;electrically and mechanically coupling a second passive component to thethird bonding surfaces.
 2. The method of claim 1 wherein the integratedcircuit is bonded to the leadframe before the first or second passivecomponents and the first and second passive components are verticallyaligned with the integrated circuit so as to mechanically shield theintegrated circuit.
 3. The method of claim 1 wherein the step ofmechanically coupling further comprises vertically aligning the firstand second passive components.
 4. The method of claim 1 wherein the stepof electrically coupling the integrated circuit, the first passivecomponent, and the second passive components comprises solder bumpbonding.